1. Field of the Invention
The invention is directed to a crane with a telescope jib having a plurality of telescoping sections which are individually moved into and out of a base jib.
2. Description of the Prior Art
In a prior art crane with telescope jib known from EP 0 661 234 A1, individual telescoping sections which can telescope out are moved out and in only by a single-stage piston-cylinder unit after locking pin connections are released, and are bolted in the respective moved out or moved in positions by locking bolts which are spring-loaded in the direction of their locked positions. A piston rod of the single-stage piston-cylinder unit is articulated at the jib articulation point which terminates the inner end of the outer section. A driver device which can be coupled with receptacles of the telescoping sections is arranged in the area of the end of the cylinder from which the piston rod emerges. The driver device comprises a hydraulic block with cylinders located on opposing sides of the hydraulic block. Bolts are formed by pistons of the cylinders and can be moved in and out, of the cylinders. A hydraulic piston-cylinder unit is arranged perpendicular to the locking bolts for actuating the respective locking bolt. The hydraulic elements of the driver device are in an operative connection such that the radially located piston-cylinder unit for pulling in the respective locking bolt can be actuated only when the driver device is coupled, via the locking bolts, with the section which is to be telescoped out or in.
A comparable prior art telescoping system is known from EP 0 754 646 A1. This telescoping system has a base section and at least two sections which can telescope relative to the base section. The sections are fixed in their respective position relative to one another by removable insertion bolts (locking bolts) penetrating the walls of adjoining sections. The telescoping system further has a, preferably single-stage, lift cylinder which is limited by the sections and which is acted upon at both sides by pressure medium. This lift cylinder is provided with drivers which can be brought into an operative engagement with the respective section to be displaced. As is the case in the prior art mentioned above, the piston rod of the piston-cylinder unit is articulated at the inner end of the outer section. Both known suggestions have the disadvantage that the oil supply to the piston-cylinder unit is carried out on the inside and long distances and with the formation of a corresponding turbulence for returning the oil supply to the oil supply storage tank. This reduces the telescoping speed. Further, the weight of the main jib head is increased by the quantity of oil located in the piston-cylinder unit, which reduces the useable load.
Another prior art crane is disclosed in DE 31 25 603 A1 including a telescope jib with a base jib and three telescoping sections which can be moved in and out directly or indirectly via chain drives by means of a single-stage piston-cylinder unit. The cylinder housing of the piston-cylinder unit is articulated by its rear end at the inner end of the base jib. The piston rod is connected at the front end, via a bolt, with a cylinder box which encloses the moved out piston rod and which is connected in the vicinity of its inner end by a bolt with the side walls of the first telescoping section. This construction is disadvantageous in that all three telescoping sections can only be moved in and out jointly and it is not possible to purposely move only one telescoping section in and out of the base jib.